1. Field of the Invention
The invention relates to a sealing device for sealing a cavity that can be rotated around a rotational axis, especially a cavity of a rotary film evaporator.
2. Description of the Prior Art
In order to evaporate substances, for example, in order to evaporate solvents during the concentration of pharmaceutical or chemical products, rotary film evaporators are used, such as for example, the commercially available rotary film evaporators made by Genser Wissenschaftliche Apparate (a scientific equipment company) based in Rothenburg o.d.T., Germany. With these known rotary film evaporators, the liquid substances to be evaporated are placed into the cavity of a rotating flask (evaporator vessel), usually in a heating bath. By rotating the flask, a thin liquid film is created on the inside of the rotating flask and the substance, especially the solvent, evaporates from said liquid film. A certain amount of the substance or of the solvent also evaporates directly out of the liquid surface in the rotating flask. The vapor is transported out of the rotating flask through a vapor line to a condenser, where it is condensed out again. In general, a negative pressure or vacuum is also generated in the rotating flask in order to increase the vapor pressure of the substances to be evaporated and in order to treat the product gently. The vapor line is connected in a passage area to the rotating flask via a rotatable connection. The connection site is sealed by means of an axial sliding ring sealing device that has a sliding ring arranged concentrically to the rotational axis on the rotating flask and a counter sealing face on the vapor line on which the sliding ring slides when the flask rotates. The sliding ring is made of a PTFE compound (PTFE/glass), the counter sealing face on which the sliding ring slides is often made of glass. However, it is also known to employ radial shaft seals, for example, radial sliding rings (shaft sealing rings) cooperating with a corresponding cylindrical counter sealing face to seal the system.
Extremely high demands are made to the sealing system of a rotary film evaporator. It has to be resistant to virtually all chemicals and has to remain leak-tight over a long period of time. Moreover, when leaks occur in the sealing system, sometimes spontaneously, the vacuum in the system deteriorates, that is to say, the pressure rises. This vacuum deterioration leads to an increase in the boiling temperature (or to a reduction of the vapor pressure) and thus to a rise in the product temperature. This is normally ameliorated by the fact that the heating bath temperature is set at a value that is not critical for the product. However, the drawback of this approach is that the evaporation performance is worse. Furthermore, as a result of a leak, product losses or even product destruction can occur, which is often associated with substantial financial losses in the case of sensitive and expensive products.
For these reasons, both sealing faces are machined mechanically precisely so that the leakiness at this sealing site is as small as possible. In the case of a sliding ring seal, there can also be an adjustment means for the sliding ring or for the opposite side in order to compensate for temperature differences and/or wear and tear of the seal. These known measures yield a final vacuum value of at least 0.1 mbar in the rotary film evaporator without any problems when a commercially available laboratory oil vacuum pump (rotary slide-valve pump) with a suction capacity of about 2500 liters per hour is used to evacuate the rotary film evaporator. EP 0,504,099 B1 discloses a rotary film evaporator with which the leak-tightness of a sealing system for carrying the vapor to the rotating flask is improved in that two tubular or annular parts are arranged coaxially to the rotational axis and adjacent to each other, whose front ends facing each other form sealing faces that slide on each other. These sealing tube parts or sealing ring parts are made of a sliding plastic, glass, ceramic or carbon material and especially of a PTFE composite material. A stationary sealing ring is additionally arranged on the outside of the lateral surface area of each of the two tubular or annular parts.
The object of the present invention is to provide a sealing device for a rotatable cavity, especially of a rotary film evaporator, with improved leak-tightness.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a sealing device for sealing a rotatable cavity that can be rotated around a rotational axis, especially a cavity of a rotary film evaporator, which comprises
a) a number nxe2x89xa72 of sealing areas that are separated from each other by nxe2x88x921 intermediate zones (interspaces) that each lie between two sealing areas and in each of which two sealing faces, which run continuously (coherently) around the rotational axis, can be moved (rotated) slidingly (abrasively, prone to wear and tear) on each other when the cavity rotates, and
b) at least one, especially lockable, connection for at least one of the intermediate zones for charging and/or discharging and/or passing fluids (vapor) into or out of or through the intermediate zone.
The present invention is based on the notion of creating at least one additional buffer zone that is located in the seal between the cavity and an outer, generally air-filled, chamber and that is in the form of an intermediate zone which, in the flow direction for fluids flowing through the seal in case of a leak, is arranged in series with respect to the other sealing areas with the flat or curved sealing faces that slide on each other. This buffer zone or these buffer zones can be flow-connected via the appertaining connection to a fluid-filled chamber or a fluid conveying means. In this manner, the interfering influence of an existing leak can be diminished or compensated for in a desired manner, for example, by generating a defined pressure, especially a negative pressure, or a defined gas atmosphere in the intermediate zone.
Alternatively, the sealing device for sealing a cavity that can be rotated around a rotational axis, especially a cavity of a rotary film evaporator, can comprise
a) at least two sealing faces that slide on each other and can be rotated opposite from each other and
b) at least one surface-pressure control element to control the surface pressure with which the sealing faces that slide on each other can be pressed against each other,
whereby
c) the surface-pressure control element has a control connection to apply a controlling quantity.
Through these measures, it is possible to compensate for wear and tear or thermal expansion behavior of the sealing faces by an automatic setting or adjustment of the surface pressure of the sealing system. The formation of a gap between the sealing faces can be avoided.
In a first advantageous embodiment of the sealing device, the sealing areas are located radially, that is to say, perpendicular to the rotational axis, at a distance from each other relative to the rotational axis. This embodiment corresponds to an axial seal or axial shaft seal that has been improved according to the invention, including, for example, an axial sliding ring seal. The intermediate zones and the sealing areas are then preferably arranged concentrically around the rotational axis, but they can also be arranged eccentrically. In addition to the preferred annular or hollow-cylindrical shape, the intermediate zones and the sealing areas can also have a different closed shape, for example, an elliptical shape. Preferably the sealing faces are aligned essentially orthogonally relative to the rotational axis.
In a second and likewise advantageous embodiment of the sealing device, the sealing areas are arranged axially relative to the rotational axis, that is to say, parallel to the rotational axis, staggered with respect to each other. This embodiment corresponds to a radial seal or radial shaft seal that has been improved according to the invention, which can be configured as a radial sliding ring seal. The sealing faces are especially configured essentially rotation-symmetrically relative to the rotational axis and preferably run parallel to the rotational axis, that is to say, in the shape of a cylindrical surface.
The sealing faces of the sealing areas are generally formed with surfaces of sealing bodies facing each other, whereby at least a first sealing body can be rotated along with the cavity (is not stationary in the reference system of the surroundings of the cavity) and at least a second sealing body cannot rotate along with respect to the cavity (is stationary in the reference system of the surroundings). The first sealing body or bodies can be formed with a wall of the cavity orxe2x80x94as a prefabricated partxe2x80x94can be connected to a wall of the cavity at the end or on the outside. In particular, at least one of the sealing bodies can be a sliding ring. The intermediate zones between the sealing areas are generally configured with recesses (dents, grooves) or openings (gaps, passages) in only one of the sealing bodies (alternately or all in the same sealing body) or in both sealing bodies, or else with interspaces between several individual sealing bodies.
In an especially advantageous embodiment, in order to seal a connection area of the rotatable cavity, the sealing device is provided with a stationary additional cavity that serves especially as a line to charge and/or discharge fluids into or out of the rotatable cavity. Therefore, the transition area between the two cavities that are rotatable opposite from each other serves especially as a fluid passage area. The second sealing body is then preferably formed with a wall of the stationary additional cavity orxe2x80x94as a prefabricated partxe2x80x94connected to a wall of the stationary additional cavity on the outside or at its end, for example, in the form of a sliding ring.
The connections can also be arranged spatially staggered with respect to the intermediate zones and are then connected to the intermediate zones by means of lines. These lines preferably run through the cavity or one of the cavities.
The connections provided according to the invention for the intermediate zones can be used advantageously in many ways.
In an especially advantageous embodiment, fluid conveying means are connected to the at least one connection of at least one intermediate zone in order to convey desired fluids into the intermediate zone or to convey fluids that are present in the intermediate zone out of the intermediate zone, or else to convey a fluid between two connections through the intermediate zone. The fluid delivery means preferably comprises a flow machine such as a pump, but can also consist of a gas or liquid reservoir (e.g. pressurized cylinder) that is under a certain pressure.
This fluid delivery can preferably be regulated, whereby preferably the connections are also regulated, that is to say, they can be at least partially closed and opened again.
Thus, via the fluid delivery means, the pressure in the at least one intermediate zone is preferably regulated, especially in order to generate a vacuum (negative pressure).
In an especially advantageous embodiment, the pressure differential between the pressure in the at least one intermediate zone (zone pressure) on the one hand, and the pressure in the rotatable cavity (internal pressure) on the other hand, can be set at or regulated to a prescribed value (setpoint, reference value).
The prescribed value of the pressure differential between the pressure in the at least one intermediate zone on the one hand, and the pressure in the rotatable cavity on the other hand, can be essentially equal to zero. Relative to the cavity and the internal pressure prevailing there, practically no more leaking can be detected.
In contrast, if the setpoint for the pressure differential is set at greater than zero, then in case of a leak, depending on the amount of the pressure differential, air flows out of the outer chamber as a result of the higher pressure prevailing there (atmospheric pressure) into the evacuated cavity. This can be tolerated as long as the air quantity flowing in is so small that it is negligible in the cavity in terms of the process technology.
In a further embodiment, the zone pressure in the intermediate zone is set so as to be less than the internal pressure in the cavity. In case of a leak, gas or vapor from the evacuated cavity enters the zone. This can either be accepted if the quantity is not too great or else preferably a collecting means is added onto the connection of the intermediate zone in order to collect and possibly reutilize the substances that have entered the intermediate zone. The collecting means can be, for example, a condensation device for condensing the vapors or an absorption device for absorbing the vapors.
In addition to an evacuation of the intermediate zones as a mode of operation (operating method) of the sealing device, it is also possible to feed fluids having the desired composition into the intermediate zone. In this manner, numerous functions can be achieved.
In a special embodiment, a liquid or gaseous coolant or heating medium is conveyed through at least one intermediate zone in order to cool or heat the sealing areas. Here, the sealing faces that lie opposite from each other can both be heated or cooled, whereby the temperatures can also be different.
Furthermore, it is advantageously possible to fill the intermediate zones with fluids that are process-neutral or process-inherent (present in the process) for a process that takes place in a rotatable cavity or in a process chamber that is connected to said cavity, especially a rotary film evaporation process in a rotary film evaporator. Examples of process-neutral fluids are inert gases such as noble gas or nitrogen or inert liquids and gaseous or liquid solvents for process-inherent fluids or other substances that are to be evaporated or that have already evaporated.
In order to improve the sliding behavior at the sealing faces that slide on each other, in another mode of operation, a sliding agent or lubricant can also be applied to these faces via the at least one intermediate zone, whereby the term fluid, in addition to liquid lubricants such as, for example, oils, is also meant to include greases and solid lubricants such as viscous pastes or the like.
Another mode of operation for the sealing device is characterized in that a cleaning fluid, for example, a solvent, is applied to the sealing faces through the at least one intermediate zone in order to remove dirt from the sealing faces and/or in the intermediate zones.
Finally, the connections of the intermediate zones can also be used to measure the pressure in the intermediate zone or zones. Then, the individual connection site is connected to a corresponding measuring means which, in turn, is preferably connected to an evaluation means in order to evaluate the measured pressure values. The evaluation can comprise especially the detection of pressure changes, which can be used as a measure of any leaks.
In order to set the surface pressure between the sealing faces, as the surface-pressure control element, in an advantageous embodiment, an expansion element that can be differently expanded in the normal direction relative to the sealing faces as a function of the controlling quantity can be used such as, for example, a pneumatic or hydraulic element that is controlled via a pressure as the controlling quantity at the control connection, an element that can be electrically controlled via a control current or a control voltage as the controlling quantity, especially an electric linear motor, or a thermal expansion element whose length depends on its temperature, whereby then a thermal quantity is used as the controlling quantity at the control connection.
In an advantageous mode of operation, a monitoring means is provided that monitors the leak-tightness at the sealing faces, especially using the intermediate zones, and that keeps said leak-tightness within a prescribed or prescribable tolerance range by controlling the surface-pressure control element.
In a cleaning or disinfecting mode, the surface pressure of the sealing faces can also be increased temporarily by means of the surface-pressure control element in order to warm up the sealing areas by means of friction.
A preferred application for the rotation seal according to the invention is in a rotary film evaporator for sealing a rotatable cavity of the rotary film evaporator, especially the rotating flask in which the substances are evaporated, or in a feed line to the rotating flask. The sealing effect here can still be additionally improved in that at least one sealing device configured as a radial seal according to the invention is arranged in series with at least one sealing device according to the invention configured as an axial seal. Moreover, this measure is also advantageous with the prior art seals when it comes to reducing leaks.